A. Field of the Invention
This invention relates to the field of Point-to-Point Protocol (PPP) and Internet Protocol (IP) data networking. More particularly, the invention relates to a process by which a communications device, for example, a laptop computer equipped with a cellular telephone modem, activates a Point-to-Point Protocol (PPP) connection to a Internet Protocol (IP) packet switched network, such as a Ethernet LAN or the Internet, via a network access server. The invention is applicable to other types of PPP links besides a wireless PPP link.
B. Description of Related Art
Wireless communications networks offer much flexibility to the user, in that they allow users of portable communications devices, such as personal digital assistants, laptop computers, telephones, and other appliances to get connected to the public switched telephone network from any location within the region served by the wireless network. Connolly et al., U.S. Pat. No. 5,325,419, discloses a personal communication system by which a mobile device uses an RF link to a communicate with an intelligent base station. The intelligent base station provides radio access along with an Integrated Services Digital Network (ISDN) interface to the public switched telephone network. The PSTN aspect of the system has three components: a personal communications switching center, where telephone central office switches have certain characteristics, a signaling transfer point, and a service control point where an intelligent data base exists maintaining certain user features and records.
The patent application of Yingchun Xu, et al., Ser. No. 08/887,313, now U.S. Pat. No. 6,151,628, which is assigned to the assignee of the present invention and which is fully incorporated by reference herein, describes a system by which a wireless communications device such as a laptop computer may access a packet-switched (e.g., IP) data network such as a corporate backbone network or the Internet. In the Xu et al. system, a frame relay line connected to the wireless network base station couples the remote wireless user to the packet-switched network via an all-digital network access server. This type of network access server can be configured as an InterWorking Unit (IWU) and the two terms are occasionally used interchangeably herein. The network access server provides an interface to the frame relay line and a base station and central base station controller in the wireless network, and an interface (including router functionality) to the packet switched IP network. The Xu et al. application further discloses certain accounting and routing techniques that permit network access to authorized users, while at the same time providing convenient authorization and accounting techniques to be performed by the entity operating the network access server. Network access servers suitable for use as an IWU platform are, per se, known in the art and commercially available from companies such as 3Com Corporation. They are also described in the patent literature. See, e.g., the patent awarded to Dale M. Walsh et al., U.S. Pat. No. 5,528,595, incorporated by reference herein.
In the prior art, every time a call is initiated over a PPP link (such as a call initiated by a remote terminal over the public switched telephone network, over a wireless network, or over some other circuit switched network to a network access server), part of the connection process involves the negotiation of certain protocols with the PPP, such as the Link Control Protocol (LCP), and Network Control Protocols (NCP). Such protocols negotiations are necessary so as to insure that both the remote terminal and the modems or other elements in the network access server are configured in a compatible manner. The many exchanges of parameters during the negotiations and subsequent data transfers contribute to establish a xe2x80x9cstatexe2x80x9d for the PPP protocols to operate within. These protocol negotiations, particularly at the time a PPP link is established, can become time consuming, relatively speaking.
The known prior art has failed to recognize that if a PPP session for a user goes dormant and the user then connects to a different IWU (or to a different port in the same IWU), that the PPP negotiated parameters and the state for a call which is currently going dormant can be used to make the new PPP connection, without repeating the lengthy PPP negotiations. An example of how a PPP session may go dormant is when a mobile wireless communications device moves out of range of a first base station and the call is handed off to a second base station. When a new PPP circuit is established from the mobile device, via the new base station, to the network access server, the network access server/IWU would go through the PPP protocol negotiation procedure in accordance with the prior art approach. In our invention, however, the PPP state from the dormant PPP session (i.e., no active data transfer but the PPP session is still active) is switched over to the new, active PPP session, without requiring re-negotiation of the PPP parameters. Moreover, the switching of the PPP state can occur without the mobile communications device having to disconnect and reconnect it""s PPP session. To the mobile unit, it is unaware that its calls have been handed off between base stations and between network access servers/IWUs. Thus, the invention can provide essentially continuous, uninterrupted access to the IP data network regardless of where the user may move within the wireless network.
The invention is especially useful in wireless networks where users with PPP connected mobile units will be continuously moving in and out of range of base stations. However, the same concepts work in any network which provides the ability to connect devices together via the PPP. For example, if a user dials up via the Public Switched Telephone Network (PSTN) and establishes a PPP link with a device such as a network access server, the session goes dormant, and then dials into a different port in the network access server, the PPP state from the dormant session can be used in the new session without the user having to renegotiate the PPP protocols.
An object of the invention is to provide a method to allow a PPP session to go dormant and then dial back into a different port on the same network access server without needing to go through the standard LCP and NCP negotiations to bring the new PPP session active.
In accordance with another feature of the invention, a method is provided to allow a PPP session to go dormant, and then the user dials back into a different port on a different network access server without requiring the user to clean up the previous PPP session on the original network access server.
In accordance with another feature of the invention, a method is provided which allows for call cost accounting for the user during active call periods, as well as during dormant call periods.
These, and other, features and advantages of the invention will be appreciated from the following detailed description of a presently preferred embodiment of the invention.
A method is provided for connecting a communications device to a packet switched network. The nature of the communications device is unimportant, and could be a personal computer, personal digital assistant, laptop computer with a cellular telephone modem, telephone, or otherwise. The method provides for the step of first initiating a Point-to-Point Protocol (PPP) session between the device and a network access server. The network access server provides access to the packet switched network for the device. The particular medium in which the PPP session is established is not critical. The example of a wireless medium described herein is only one possible example. The session is associated with a PPP state and with a first port in the network access server. As some later point in time, the PPP session thereafter becomes dormant, but the PPP state is not removed from the network access server.
In a first embodiment of the invention, after the PPP session has become dormant, the network access server receives a new call set-up message associated with the communications device. The new call set-up message arrives at a second port in the network access server. In the wireless example, the user operating the lap-top computer moves out of range of one radio tower and into range of another tower, and a call set up message and PPP session is initiated between the new radio tower, base station and the new (second) port in the network access server.
Rather than re-negotiate the PPP protocols (LCP and NCP) for the new session, the PPP state is switched from the dormant PPP session associated with the first port to the session associated with the second port in the network access server. Thus, the PPP state is transferred to the PPP session associated with the new call set-up message and the negotiation of link control protocols or network control protocols between the device and the network access server may be avoided.
In one possible example, the first PPP session becomes dormant due to movement of the communications device relative to a first radio tower linking the device to a wireless communications network. The new call set-up message is initiated in response to the device coming within range of a second radio tower in the wireless communications network.
In one possible embodiment of the invention, the new call set-up message contains information uniquely identifying the device (such as an International Mobile System Identification number (IMSI) and/or Electronic Serial Number (ESN)). The method further comprises the steps of transmitting an access-request message containing this information from the network access server to an authorization server. The authorization server, for example a RADIUS authentication, authorization and accounting server, responsively issues an access-accept message to the network access server if the device is authorized to access the packet-switched network (e.g., the user of the device is a subscriber to the service, has paid its bills, etc.). The network access server then uses the information uniquely identifying the device to identify and find the dormant PPP session associated with the first port in the network access server. For example, the network access server may contain a general purpose computing engine and memory maintaining a table mapping ISMI/ESN numbers to a particular port, with the table indicating whether the particular port is active or dormant. In this fashion, the network access server can avoid re-negotiation of the PPP protocols and instead use the PPP state from the dormant session.
The invention can be used when a connection between the communications device and a second network access server is initiated, while a dormant PPP session exists for the device in the first network access server. In this example, a PPP session is initiated between the device and a first network access server. The first network access server provides access to the packet-switched network for the device. The session is associated with a PPP state and with a first port in the first network access server. The PPP session thereafter becomes dormant but the PPP state is not removed from the network access server.
Thereafter, a second network access server receives a new call set-up message containing information uniquely associated with the device. The new call set-up message arrives at a port in the second network access server. The second network access server transmits an access-request message to an authentication server. The access-request message contains the information uniquely identifying the device, such as the IMSI/ESN number for the device.
The authorization server responsively issues a message to the first network access server to initiate clearing of the dormant session from the first network access server. The first network access server transfers the PPP state for the mobile device to the second network access server. The authorization server further issues an access-accept message to the second network access server. The second network access server responsively enables the negotiation of protocols associated with the PPP, or, more preferably, uses the transfer of the existing PPP state from the first network access server and avoids the re-negotiation of the PPP protocols.
A method is also provided for accounting for wireless communication periods between a mobile communications device and a packet-switched network. The device is coupled to the packet-switched network via a network access server. The method involves tracking time periods in which a communications session between the device and the packet-switched network is dormant. In a preferred embodiment, the step of tracking comprises the step of periodically sending an update message from the network access server to an accounting server. The update message includes information uniquely identifying the device and information indicating the dormant status of the session. The accounting server (e.g., a RADIUS server) monitors the update messages and maintains a log of the amount of time that the session is dormant. Further, the accounting server (or other device in the system providing wireless access to the network) allocates a cost for the dormant time periods. In similar fashion, the accounting server keeps track of the time periods in which the sessions are active, and allocates a cost to the active time periods. The organization operating the network access server and providing wireless access to the network bills the user for both the dormant time periods and the active time periods.